1. Field of the Invention
This invention relates to electrical switching apparatus such as protective devices and switches used in electric power distribution circuits carrying large currents. More particularly, it relates to such apparatus which uses a large compression spring for closing, and to a clutch assembly for controlling the discharge of energy in the close spring.
2. Background Information
Electrical switching apparatus for opening and closing electric power circuits typically utilize an energy storage device in the form of one or more large springs to close the contacts of the device into the large currents which can be drawn in such circuits. Such electrical switching apparatus includes power circuit breakers and network protectors which provide protection, and electric switches which are used to energize and deenergize parts of the circuit or to transfer between alternative power sources. These devices also include an open spring or springs which rapidly separate the contacts to interrupt current flowing in the power circuit. As indicated, either or both of the close spring and open spring can be a single spring or multiple springs and should be considered as either even though the singular is hereafter used for convenience. The open spring is charged during closing by the close spring which, therefore, must store sufficient energy to both over come the mechanical and magnetic forces for closing as well as charging the open springs. Moreover, the closing spring is required to have sufficient energy to close and latch on at least 15 times the rated current.
Both tension springs and compression springs have been utilized to store sufficient energy to close the contacts and to charge the open spring. The tension springs are easier to control, but the compression springs can store more energy. In either case, a robust operating mechanism is required to mount and control the charging and discharging of the spring. The operating mechanism typically includes a manual handle, and often an electric motor, for charging the close spring. It also includes a latch mechanism for latching the close spring in the charged state, a release mechanism for releasing the stored energy in the close spring, and an arrangement, a pole shaft for example, for coupling the released energy into the moving conductor assembly supporting the moving contacts of the switch.
Because the closing spring is designed to function at 15 times the rated current, it is possible that, when closing on a moderate current, the spring will release enough energy to over-rotate the cam shaft. When the cam is over-rotated a small amount of energy is transferred back into the spring. At this point energy in the spring will cause the cam shaft to reverse and turn backward past the contact closed position. When this happens, the breaker contacts begin to reopen which may cause damage from arcing. The cam may continue to rotate and counter-rotate until equilibrium is reached.
Thus, there is room for improvement in electrical switching apparatus of the above types and particularly in the operating mechanism which controls the discharge of the close spring.
Particularly, there is a need for a simple one-way clutch assembly for the operating mechanism of such apparatus which prevents, reverse rotation following discharge of the close spring.
There is yet another need for such an operating mechanism which is easy and economical to manufacture and assemble.